Piezoelectric apparatus



July 25, 1939. HAASE 2,167,506

PIEZOELECTRIG APPARATUS Filed March 22, 1958 .52 veni or/ f/ieaaor l/aase Patented July 25, 1939 UNITED STATES PATENT OFFICE PIEZOELEGTRIC APPARATUS Application March 22, 1938, Serial No. 197,426 In Germany March 16, 1937 4 Claims.

The invention relates to piezoelectric apparatus and particularly to quartz and other piezoelectric crystal holders suitable for electrical vibrating systems.

It is well known to clamp quartz and other piezoelectric crystals between two electrodes in such a manner that there is an airgap between the quartz crystal and the electrode or electrodes. The properties of vibration of such crystals may be varied by adjusting the width of such airgaps. As based upon this apprehension, quartz holders have been constructed which permit the airgap to be adjusted at will. However, this problem involves certain difficulties since specific holding means are required if the electrodes are not integral with the piezoelectric crystal. It has been proposed either to support the crystal by the aid of projections at points of its major face remote from its centre, or to place the quartz crystal on one of the electrodes and to provide one of the two electrodes movable. The first mentioned arrangement requires a certain thickness of the quartz crystal and is therefore unuseful in operation at short wavelengths where very thin crystals must be employed. The second proposition which is applicable even in connection with small crystals requires the crystal to be horizontally supported. In piezoelectric constructions of less accuracy, the quartz crystal may have a given freedom of motion within the space between the two electrodes, but this expedient obviously gives rise to changes in the natural frequency of the crystal.

These and other difficulties are avoided by virtue of the novel arrangements according to the invention, the main feature of which consists in the fact to provide one or both electrodes of the piezoelectric quartz plate in the shape of resilient plates and to provide a number of distributed point or cup-shaped projections on one surface at points remote from its centre, said projections being adapted to continuously maintain the quartz plate under pressure. It is thus possible to adjust the airgap by varying the pressure applied to the portion in the centre of the projections of the resilient plate.

The invention will be fully understood from the following description taken in conjunction with the accompanying drawing, in which:

Fig. 1 is a side elevation partially in section of one embodiment according to the invention; while Figs. 2 and 3 are modifications of the representation shown in Fig. 1.

With reference to Fig. 1, I denotes a quartz plate and 2 and 3 the electrodes thereof. The

electrode 2 is made as a resilient plate in accordance with the invention and carries at points remote from its centre a number of cup-shaped projections 4, e. g. four thereof, which maintain a quartz plate I under pressure. The electrode 3 is illustrated as a rigid member in this embodiment. The opposite face of the resilient electrode 2 carries at its centre portion a metallic member against which the point of a screw 5 abuts. This screw may be tightened or loosened whether the airgap is to be made larger or smaller. The cup-shaped projections above specified may be replaced by point-shaped means as shown in Fig. 3. These may be formed by bending the corners of a rectangular plate at 90 degrees. The number of projections employed is irrelevant, but the provision of three such projections involves the particular advantage that all such projections exert the same pressure upon the piezoelectric crystal.

Fig. 2 illustrates a modification over the arrangement shown in Fig. 1, but the only difference is that the rigid electrode 3 of Fig. 1 has been substituted by a resilient electrode 2 according to the invention. The plate I is thus clamped from both sides in exactly the same manner as described for one side in connection with the arrangement of Fig. 1.

What is claimed is:

1. In an electromechanically vibratory apparatus, a piezoelectric body, a rigid electrode adjacent to one face of said piezoelectric body, a plate-shaped resilient electrode carrying at one of its surfaces and remote from its centre a number of distributed projections which abut against the other face of said piezoelectric body, and means for applying a pressure to the opposite surface of said plate-shaped resilient electrode in order to vary the airgap between said electrode and said piezoelectric body.

2. In an electromechanically vibratory apparatus, a piezoelectric body, plate-shaped resilient electrodes, each electrode carrying on one of its surfaces and remote from its centre a plurality of distributed projections which abut against said piezoelectric body, and means for applying a pressure to the opposite surfaces of said plateshaped resilient electrodes in order to vary the airgaps between said electrodes and said piezoelectric body.

3. In an electromechanically vibratory apparatus according to claim 2, in which said projections are cup-shaped means.

4. In an electromechanically vibratory apparatus according to claim 2, in which said projections are point-shaped means.

THEODOR I-IAASE. 

